# What makes dynamical decoupling a good method since the fidelity after using it can only reach 0.85 or so?

From this paper, I see that the fidelity of single qubit gate after using dynamical decoupling only reach around 0.85 while I normally saw experiment papers state their fidelity can reach around 0.99 to be a good result. So my question is, does 0.85 a good fidelity with the method of dynamical decoupling, if so, I think this fidelity is a little bit low?

The authors are estimating the fidelity of the time-evolved state with the initial state $$|\psi\rangle$$. If you prepare a state $$|\psi\rangle$$, and not do anything, it will (among other things) decohere such that the fidelity of the time-evolved state with $$|\psi\rangle$$ decreases with time. In particular, it is not surprising that you don't find great fidelities if you wait long enough. The purpose of dynamical decoupling is to counter-act this, at least to some extent, and that's what's presented in this plot.